1. Field of the Invention
The present invention relates to a large bottle made of synthetic resin, and, more particularly, relates to the body wall structure of a large square bottle made of biaxially oriented blow molded polyethylene terephthalate (hereinafter referred to as "PET"). The structure of the bottle including the body upper end to a shoulder and the wall structure of a ridge-line portion provides a significant influence upon the external appearance and configuration of the bottle by bending and connecting two wall surface portions.
2. Description of Related Art
The biaxial oriented blow molded bottle of polyethylene terephthalate resin has excellent durability in various areas such as content resistance, chemical resistance, weather resistance, shock resistance and the like. Such a bottle also exhibits high mechanical strength, transparency, no pollution and gas barrier properties. Therefore, this type of bottle has been used on a large scale for containing various kinds of liquid.
However, the PET biaxial oriented blow molded large bottle does not have sufficient mechanical strength in its body, such as self configuration sustaining capability or buckling strength, since the body is a main portion of the bottle and is thin in thickness. Particularly, a bottle having a square tubular body is poor in not only buckling strength but also self configuration sustaining capability. Therefore, large depressed deformations tend to occur in the body which are caused by negative pressure generated within the bottle after a liquid is contained and sealed therein.
In order to solve such problems in a square-shaped PET bottle, a central circumferential groove is provided at a substantial center of the body for increasing buckling strength against depression force applied on the bottle from the outside and for increasing self configuration sustaining capability of the body against external forces applied in the diametrical direction. At the central portion of a flat wall on the body, divided into upper and lower portions by a central circumferential groove, a recessed portion is provided having a depression deformable shaped panel wall as a bottom wall for taking up negative pressure generated in the bottle by a certain depression deformation at the shaped panel wall to prevent any depression deformation from occurring in the body and to increase self configuration sustaining capability of the flat wall portion.
An increase in mechanical configuration sustaining capability by providing a central circumferential groove and a recessed portion formed with the shaped panel wall can be obtained by adding inclined groove sidewalls in the central circumferential groove and inclined groove sidewalls in the recessed portion as reinforcing rib wall pieces with respect to the diametrical direction of the body.
Therefore, hitherto, in order to increase the function of inclined groove sidewalls and recess sidewalls of the central circumferential groove and the recessed portion as reinforcing rib wall pieces, oblique angles of the groove sidewalls and recessed sidewalls with respect to the central axis of the bottle have been set to large values.
The self configuration sustaining capability of the body of the bottle, particularly the vicinity of the central circumferential groove grasped by the hand is actively reinforced by setting the oblique angles of the grooved sidewalls and recessed sidewalls at large values. However, when more than a certain pressure is applied to the body of the bottle at the time of handling or at the time of casing and transporting bottles, the wall portion extending from the groove sidewalls and recessed sidewalls to the flat wall is sharply bent and/or depressedly deformed. Further, the deformed portion will not return to the original configuration even if the pressure is removed, and the bent and/or depressed deformation then becomes a permanent deformation which causes the commercial value of the bottle to be lost.
The above-described conventional negative pressure accommodating recessed portion is constructed by forming the shaped panel wall with a bottom wall having a shape which is easily deformable by negative pressure and absorbing negative pressure generated in the bottle by a large depressed deformation at the central portion of the shaped panel wall. However, the negative pressure deformation of this shaped panel wall detracts from the external appearance of the bottle, which lowers the aesthetic appearance and style of the bottle as a consumer good.
Moreover, the shaped panel wall occupying a large surface area at each flat wall of the body is liable to deform. So, when grasping the bottle by the hand, the deformed panel wall where finger tips contact is easily deformed, and the bottle becomes unstable to handle by hand.
Furthermore, as described above, the shaped panel wall occupies a large surface area of each flat wall of the body, but the wall structure of this shaped panel wall is mainly a deformable flat structure. Thus, the bottle's external appearance becomes simple, which also makes the external appearance of the bottle dull.
As stated above, the concave and convex shaped panel wall is molded at the flat wall portion of the body of a PET large square bottle, so that it is extremely difficult to print a commercial name or a company name or to stick and display a label. Hence, the commercial name or the company name is displayed with the aid of a shrunk label made of a heat-shrinkable sheet.
Since this shrunk label is originally a simple sheet, it is easy to print patterns and to form the label onto a cylindrical body. It is further advantageous to strongly attach a label to the bottle by simple but secure heat treatment. However, because of certain shrinking deformation of a heat-shrinkable sheet, the portion opposed to the flat wall of the square tube has large shrinkage as compared with the portion opposed to the ridge-line. As a result, the end of a shrunk label wound around the bottle is wrinkled which deteriorates the external appearance and style of the goods.
When the shoulder portion extension is not sufficient as compared with the square tubular body, a large difference of extension is generated between the ridge line of the shoulder and the flat wall portion, resulting in incorrect thermal deformation at the shoulder portion by this non-uniform extension.
Among numerous characteristics inherent to the above PET bottle, transparency is extremely excellent and effective for increasing visibility of the goods.
Thus, the PET bottle has excellent transparency. As compared with a glass bottle exhibiting the same excellent transparency however, the PET bottle is simply clear and does not exhibit any crystal effect due to deflection of transmitted light, so as to be poor in visual change.
One of the principle reasons why a crystal effect is low in the PET bottle having excellent transparency is because the PET bottle is a biaxially oriented blow molded good, so that its thickness is thin and transmitted light cannot sufficiently be deflected.
It has therefore been considered to make the PET bottle thick to provide a sufficient crystal effect. However, if the PET bottle is made thicker, expensive PET material is increased in the amount required for molding one product, and, as a result, a unit price becomes high, biaxially blow molding techniques become extremely difficult, and sufficient transparency cannot be obtained without biaxially oriented deformation.